The present invention relates to manufacturing method and apparatus for a semiconductor device. More particularly, it relates to manufacturing method and apparatus for a semiconductor device in which a resist pattern is formed on a semiconductor substrate.
In accordance with improved density and integration of a semiconductor device, there are increasing demands for finer processing techniques in these days.
As means for attaining the fine processing in the lithography process, a technique for forming a resist pattern out of a chemically amplified resist utilizing generation of an acid by using, as exposing light, DUV light emitted by an excimer laser as a light source or light with a short wavelength such as EB and X-rays has recently been developed.
Furthermore, since the manufacturing process of a semiconductor device always includes pattern formation which is less refined, a resist pattern is formed also out of a conventional resist other than the chemically amplified resist (hereinafter referred to as a "non-chemically amplified resist").
Now, pattern formation using a chemically amplified resist and pattern formation using a non-chemically amplified resist in a conventional method of manufacturing a semiconductor device will be described with reference to FIGS. 10 through 14.
First, the pattern formation using a chemically amplified resist will be described with reference to FIGS. 10, 11(a) and 11(b).
FIG. 10 shows a process flow of the resist pattern formation using a chemically amplified resist, and FIGS. 11(a) and 11(b) show the state of a surface of a semiconductor substrate obtained by the resist pattern formation using a chemically amplified resist.
As is shown in FIG. 11(a), a surface of a semiconductor substrate 1 of silicon is supplied with hexamethyldisilazane (hereinafter referred to as HMDS) serving as a surface treatment agent, thereby making the surface of the semiconductor substrate 1 hydrophobic. Thus, the adhesion of the semiconductor substrate 1 is improved. This surface treatment is carried out by bubbling HMDS in a liquid phase with a nitrogen gas and spraying the resultant HMDS for 30 seconds onto the surface of the semiconductor substrate 1 having been heated up to 60.degree. C. As a result, H in OH groups existing on the surface of the semiconductor substrate 1 is substituted with Si(CH.sub.3).sub.3 (i.e., a trimethylsilyl group) as is shown in FIG. 11(b), thereby making the surface of the semiconductor substrate 1 hydrophobic. Thus, the adhesion of the semiconductor substrate 1 is improved as well as NH.sub.3 (ammonia) is generated.
Then, the surface of the semiconductor substrate 1 is coated with a chemically amplified resist so as to form a resist film. The resist film is exposed by using a desired mask, and is then subjected successively to post exposure bake (hereinafter refereed to as the PEB) and development. Thus, a resist pattern is formed.
Next, the pattern formation using a non-chemically amplified resist will be described with reference to FIGS. 12, 13(a) and 13(b).
FIG. 12 shows a process flow of the resist pattern formation using a non-chemically amplified resist, and FIGS. 13(a) and 13(b) show the state of a surface of a semiconductor substrate obtained by the resist pattern formation using a non-chemically amplified resist.
First, as is shown in FIG. 13(a), a surface of a semiconductor substrate 1 of silicon is supplied with HMDS serving as a surface treatment agent, thereby making the surface of the semiconductor substrate 1 hydrophobic. Thus, the adhesion of the semiconductor substrate 1 is improved. This surface treatment is carried out by bubbling HMDS in a liquid phase with a nitrogen gas and spraying the resultant HMDS for 30 seconds onto the surface of the semiconductor substrate 1 having been heated up to 60.degree. C. As a result, H in OH groups existing on the surface of the semiconductor substrate 1 is substituted with Si(CH.sub.3).sub.3 (i.e., a trimethylsilyl group) as is shown in FIG. 13(b), thereby making the surface of the semiconductor substrate 1 hydrophobic. Thus, the adhesion of the semiconductor substrate 1 is improved as well as NH.sub.3 (ammonia) is generated.
Next, the surface of the semiconductor substrate 1 is coated with a none-chemically amplified resist so as to form a resist film. The resist film is exposed by using a desired mask, and is then subjected successively to the PEB and the development. Thus, a resist pattern is formed.
FIG. 14 is a schematic sectional view of the resist pattern 6 of a chemically amplified resist obtained by the former pattern formation, wherein an insoluble skin layer 7 is formed on the surface of the resist pattern 6. Such an insoluble skin layer 7 formed on the surface of the resist pattern 6 can cause dimensional variation of the resist pattern 6 and etching failure in following procedures, resulting in decreasing a yield of the semiconductor device. In contrast, the resist pattern of a non-chemically amplified resist does not have such a disadvantage because no insoluble skin layer is formed thereon.
An alkali component is regarded as a factor in forming the above-described insoluble skin layer 7 on the surface of the resist pattern 6 of a chemically amplified resist. Specifically, when an alkali component exists on the surface of the resist pattern 6, an acid generated through the exposure is deactivated, resulting in forming the insoluble skin layer 7. As a result, the surface of the resist pattern 6 is formed into a T-top shape. This is understandable also in consideration of a report that a pattern cannot be resolved when a large amount of an alkali component is included (S. A. MacDonald, et al., Proc. SPIE, Vol. 1446, p. 2 (1991)) as well as in consideration of a fact that no insoluble skin layer is formed on the resist pattern of a non-chemically amplified resist.
In order to find the cause of generation of an ammonia component, that is, an alkali component harmfully affecting a chemically amplified resist, the present inventors analyzed impurities included in the atmosphere in a clean room. As a result, it was found that there is positive correlation between a concentration of trimethylsilanol, that is, a decomposition of HMDS, and a concentration of ammonia in the atmosphere as is shown in FIG. 15. On the basis of this finding, it is considered that an alkali component harmfully affecting the formation of a pattern of a chemically amplified resist derives from HMDS used as a surface treatment agent for a semiconductor substrate.
Then, the surface of a semiconductor substrate was treated with a surface treatment agent which does not generate an alkali component, and a resist pattern was formed out of a chemically amplified resist on this semiconductor substrate. As a result, although the insoluble skin layer could be reduced as compared with the case where a resist pattern of a chemically amplified resist is formed by the conventional method, the insoluble skin layer was still formed.